Walk-behind lawnmowers with weed trimmer attachments have been known for some time. These weed trimmers are convenient for cutting grass and weeds along a fence for example. These weed trimmers are usually mounted to the forward corner of a lawnmower where they can be easily seen and guided by the user of the lawnmower. A weed trimmer mounted to a lawnmower is considered to be a very useful tool.
Examples of the weed trimmers mounted on walk-behind lawnmowers have been found in the prior art and are listed herein below to show the work of others in this field and the evolution of this technology:    U.S. Pat. No. 3,668,845 issued to James M. Parker on Jun. 13, 1972;    U.S. Pat. No. 3,782,085 issued to James M. Parker et al., on Jan. 1, 1974;    U.S. Pat. No. 4,152,882 issued to Tyson W. Howard on May 8, 1979;    U.S. Pat. No. 4,551,967 issued to Joseph S. Murcko on Nov. 12, 1985;    CA Patent Appl. 2,002,351 issued to Glenn W. Gregory on Nov. 2, 1989;    U.S. Des. Pat 304,728 issued to Peter V. Piorkowski on Nov. 21, 1989;    U.S. Pat. No. 4,896,488 issued to Larry A. Duncan et al. on Jan. 30, 1990;    U.S. Des. Pat. 311,009 issued to Robert W. Wilkins on Oct. 2, 1990;    U.S. Pat. No. 5,226,284 issued to John. C. Meehleder et al. on Jul. 13, 1993;    U.S. Des. Pat. 359,291 issued to Albert J. Tihonovich on Jun. 13, 1995;    U.S. Pat. No. 5,966,914 issued to Thomas R. Reents on Oct. 19, 1999.
The weed trimmers described in the above documents are mounted to walk-behind lawnmowers. When a cutting blade on the weed trimmer needs to the replaced, it is relatively easy to tilt the lawnmower on its side; take the weed trimmer head apart and to change the tines or the cutting blades that are worn out.
Because of the way cutting blades are retained to a weed trimmer head, it will be appreciated that the maintenance and repair of a weed trimmer attachment becomes a challenge when it is permanently mounted to a lawn tractor. A lawn tractor is relatively heavy and stable on the ground. It is impractical to tilt a lawn tractor on its side to replace worn cutting blades on a weed trimmer attachment. For that reason, basically, very few weed trimmer attachments exist for mounting to a lawn tractor.
In spite of the above-mentioned inconveniences, the prior art includes at least two examples of a weed trimmer mounted to a lawn tractor: U.S. Pat. No. 5,167,108 issued to Joseph J. Bird on Dec. 1, 1992. This document describes a weed trimmer that is mounted to the side of a lawn tractor. The document does not explain how the spool of whip line on this weed trimmer is repaired or replaced.
U.S. Pat. No. 7,028,455 issued to Violet M. Liguras on Apr. 18, 2006. This document describes a mounting bracket for removably retaining a portable weed trimmer to the side of a lawn tractor. The mounting bracket has a pivot therein so that the weed trimmer can be guided by one hand in a cutting position alongside the tractor by the operator sitting on the lawn tractor. Maintenance of the cutting line is done by taking the weed trimmer altogether out of the mounting bracket and replacing the whip line reel as one would normally do with any portable weed trimmers of that type.
A search of the prior art has also shown weed trimmer heads in which the cutting blades can be replaced when the weed trimmer heads are sitting low on the ground without giving access under the sole plates of the devices. The following four documents explain the structures of these weed trimmer heads.
U.S. Pat. No. 6,119,350 issued to James W. Sutliff et al. on Sep. 19, 2000. This cutting head has replaceable cutting blades that are mounted on pivot pins. The pivot pins are retained fixed to a lower circular plate. An upper plate has holes to register with the upper ends of the pivot pins. Latch members are provided on the upper plate to engaged with the pivot pins. In use, these latch members are held in place by centrifugal force. When the latch members are disengaged, the upper plate may be lifted upward to expose the end of the pivot pins so that the cutting blades can be removed and replaced.
U.S. Pat. No. 7,614,153 issued to Lauro Guerra on Nov. 10, 2009. This document discloses a weed trimmer head wherein the cutting blades are pivoted on pins affixed to a lower shell. An upper shell above the pins keeps the blades captive on the pivot pins. This upper shell is retained to a central housing by the engagement of fingers into corresponding notches. A spring inside the upper shell must be compressed to disengage the fingers from the notches and to expose the pivot pins so that the cutting blades can be replaced.
U.S. Pat. No. 7,878,097 issued to Gordon Strader on Feb. 1, 2011; and US Patent Application 2011/0232109 filed by Gordon Strader and published on Sep. 29, 2011. These two documents describe various aspects of a weed trimmer head wherein the blades are mounted to respective pivot pins extending from a lower shell. A ring plate above the blades and the lower shell retains the blades on the pivot pins. This ring plate has slots in its circumference. The ring can be rotated to align and register the slots over the pivot pins and to provide sufficient clearance to remove the cutting blades from the pins and to replace the cutting blades.
Although the weed trimmers of the prior art that are susceptible of mounting to a lawn tractor deserves undeniable merits, it is believed that these devices contain many movable parts requiring a certain amount of clearance to operate satisfactorily. Because of these clearance, basically, these devices are subject to vibration in use, and accelerated wear due to this vibration. Therefore, it is believed that there is a market need for a sturdier weed trimmer head with less moving parts and less clearance between the parts. It is believed that there is a market demand for a weed trimmer head that is sturdy, easily maintained and more compatible to a mounting to a lawn tractor.